Scientists are working on ways to cut the risk of blood clots following treatment to unblock clogged arteries.

Stents, which are tiny tubes used to hold open the diseased blood vessels of heart patients, can themselves become blocked following treatment.

A team from Germany reports success in The Lancet with a new biodegradable prototype. And an Irish team is to begin testing a new coating for stents.

Experts welcomed the findings but said more work was needed.

Treating clogged arteries

To improve blood flow through clogged heart blood vessels, a balloon is inflated inside the artery.

This treatment - angioplasty - improves the blood supply to the heart muscle, which helps prevent angina and heart attacks.

Once the balloon is withdrawn stents are inserted to prevent the artery from re-narrowing. The need for stenting is only temporary, but current metal stents remain in place for life.

There is a risk that blood clots can occur within the stent and re-block the artery.

Such events are rare, but can be life threatening.

New developments

The stents tested by an international team led by Professor Raimund Erbel of the West German Heart Centre Essen, are made from biodegradable magnesium.

Within four months of fitting they can dissolve and completely disappear, which the scientists reason will eliminate the risk of stent re-blockage.

In tests, the biodegradable stents worked as well as conventional metal stents over 12 months, The Lancet reports.

They were also safe - none of the 63 patients had heart attacks or developed a clot where the stent had been.

Almost half of the patients had new blockages elsewhere in their arteries which would need treatment.

This research shows that absorbable stents can be used as a safe alternative in the future

Professor Peter Weissberg

But this is expected in heart patients because of the poor general state of their arteries and is unrelated to the type of stent used.

Meanwhile, Professor Jim McLaughlin and colleagues in Ulster have developed a 3D plasma coating technique for stents, and are now preparing to test it in clinical trials.

The stents, only a few millimetres wide, are covered in a diamond-like carbon structure.

This forms a coating which is theoretically smooth enough to repel the proteins which could form clots.

Professor McLaughlin said some forms of carbon were already well-known implant materials used for heart valves.

He said: "Our group are now seeking to further develop and even commercialise the 3-D plasma-coating technique, which has already shown to be highly biocompatible and promising with regards to its mechanical properties."

Professor Peter Weissberg, medical director at the British Heart Foundation, said: "This research shows that absorbable stents can be used as a safe alternative in the future, allowing the blood vessel to repair itself before the scaffold dissolves.

"But before they can be used in routine practise, further research is needed to refine the stents to get the best result."